The Drupal "White Screen of Death" or WSOD for short, would be a hilariously named aspect of Drupal if it wasn't actually an incredibly frustrating part of developing with this CMS. Unfortunately it is something that you can encounter when deploying updates for Drupal modules or when developing a new module of your own.
Occasionally a site user or developer will navigate to a page and suddenly the page content disappears, and it becomes blank. No content. No errors. Nothing. This happens sometimes, It could happen after updating a module, theme, or Drupal core. This is what is referred to by most members of the Drupal community as the White Screen of Death or WSOD. There are several reasons why this might occur, and therefore several possible solutions to the issue.
There are various steps to help you determine the cause of the WSOD such as enabling more robust error reporting, etc. but sometimes a WSOD can make it so your Drupal website is completely locked down. For example, if the error that is causing the Drupal white screen of death originated from a custom module you were developing, and the Drupal code that is problematic is cached, you may not be able to easily clear the cache in order to propagate the fix for the error. trying to use the Drush command "drush cc all" (for clear cache all) or going to the Performance settings page to manually clear the cache, will both likely fail.
Manually Empty Database Tables
If you are familiar with working with MySQL or even using tools like PHPMyAdmin, one step you can take is to go into the database and manually empty or "truncate" the tables labeled as "cache" for the Drupal website's database. This is more of an advanced technique, and is not really recommended unless you know what you're doing or you have no other alternative. At the very least, be sure to make an update of your Drupal website database before proceeding.
Drush SQL Commands
If you can't get around manually truncating those cache tables in your database, but don't want to go into MySQL directly and are concerned about potential human error while messing around with the database tables, or simply don't have permissions for direct access to the Drupal database, another alternative is to use the Drush command to truncate the table "cache".
Summary of Options
(If clearing the cache normally with Drush or the UI isn't possible)
- Empty or truncate the cache tables in the Drupal database through MySQL or PHPMyAdmin
- Empty or truncate the cache tables in the Drupal database with a Drush command
Using these techniques, you should be able to get your Drupal website to respond again after resolving the error that was causing the "white screen of death" in the first place. And if you are lucky, sometimes just clearing the cache is enough to fix the problem anyway. Just be sure to test your Drupal updates so that when these kinds of problems happen, that occur in a testing environment instead of your live website!